1. Field of the Invention
The invention relates to an electrochemical storage cell of the alkali metal and chalcogen type with at least one anode chamber to receive the anolyte and a cathode chamber to receive the catholyte, which chambers are separated from each other by an alkali ion-conducting solid-electrolyte wall and are confined, at least in part, by a metal wall, a first current collector is an electrode brought from the outside into the reactant chamber defined by the solid-electrolyte wall, and a second current collector is in part formed by the metal wall.
2. Description of the Prior Art
Rechargeable cells with solid electrolytes are highly suitable for building storage batteries with a high energy and power density. The electrolytes used in the alkali/chalcogen cells are made, for instance, of .beta.-aluminum oxide, and are distinguished by the feature that the partial conductivity of the mobile ion is very high and the partial conductivity of the electrons is several orders of magnitude smaller. Through the use of such an electrolyte practically no internal discharge takes place, since the partial electron conductivity is negligible and also the reaction substances cannot get through the electrolyte as neutral particles. An example for such a cell is a sodium/suflur cell with .beta.-aluminum oxide as the electrolyte. It is a further advantage of such a cell that no electrochemical secondary reactions occur during charging. The reason is again that only one king of ion can get through the electrolyte. The current yield, i.e., the Faraday efficiency of a sodium/sulfur cell, is therefore nearly 100%. In constrast thereto, electrochemical parallel reactions are possible in cells with aqueous electrolytes. In lead storage cells, processes leading to the dissociation of water occur during charging, in addition to the processes responsible for the charging. The Faraday efficiency is here, for instance, about 90% or less. In addition, a lead storage cell continuously loses capacity (self-discharge). Sodium/sulfur cells therefore have considerable advantages over storage batteries with liquid and in particular, aqueous electrolytes.
However, the mentioned advantages are also accompanied by a disadvantage. This is that in a battery of series-connected electrochemical storage cells, the cells with the smallest capacity determine the capacity of the entire battery. If, for instance, a partially discharged cell is incorporated into a battery in which the other cells are fully charged, there is no possibility of bringing this cell up to the same charging state as the other cells, since the latter acquire a high resistance in the charged state and thereby prevent further charging. The consequence thereof is that the capacity of the battery is reduced by the missing amount of charge. In order to compensate for this disadvantage, several cells are first connected in parallel in the assembly of a battery of solid-electrolyte cells. A high voltage is achieved by series-connecting such groups of several parallel-connected cells. Thereby, for statistical reasons, the capacity of the cell groups varies less than the capacity of single cells. In addition, equalizing currents can flow between parallel-connected cells; these take care that after some time, all cells of a group are at the same charging state.
With the present state of the art, however, there is a serious obstacle against such a connection of parallel-connected cells. This is due to the fact that the most frequent cause of failure of sodium/sulfur cells is that breaks or cracks occur in the solid electrolyte. As a result, sodium polysulfides are formed by chemical reactions of sodium and sulfur, i.e., the cell is chemically irreversibly discharged, heat being developed. Such a defective cell no longer delivers voltage and has a very low resistance. As a consequence, the other parallel-connected cells are discharged very rapidly, so that in this manner the entire group fails.